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Figure A · 1 shows a block diagram of the MIMO-OFDM receiver employing the turbo equalizer. The turbo equalizer iterates signal detection and channel decoding by exchang- ing log likelihood ratio (LLR) of coded bits denoted by λ 1 and λ 2 , respectively. Since the proposed method can im-
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This paper proposes a new MIMO-OFDM precoding technique that aims to minimize a bit error rate (BER) upper bound of the maximum likelihood detection (MLD) in mobile radio communications. Using a steepest descent algorithm, the proposed method estimates linear precoding matrices that can minimize the upper bound of BER under power constraints. Since...
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Citations
... With the perfect CSI, a MBER precoder in [3], [4] shows excellent BER performance and can outperform the MMSEbased precoder in [5], [6] and the minimum distance-based precoder in [7]. However, the perfect CSI is rarely available in practice because CSI usually incurs various impairments such as channel estimation and quantization errors. ...
... However, the perfect CSI is rarely available in practice because CSI usually incurs various impairments such as channel estimation and quantization errors. Since the imperfect CSI degrades the precoding gain of the MBER precoder in [3], [4], precoding methods that can cope with the imperfect CSI are required [8]- [10]. Precoders in [8], [9] are designed for the linear receiver, and thus are inefficient when the nonlinear receiver such as MLD is employed. ...
... It employs a Bayesian approach in formulating a framework for robust precoding. However, since it assumes a suboptimal precoding matrix structure in order to simplify a highly complex optimization process, it gains only small BER improvement over the spatial multiplexing even when the perfect CSI is available [3], [4]. ...
This paper proposes a minimum BER (MBER) based precoder that is robust to imperfect channel state information (CSI) for MIMO-OFDM mobile communications. The proposed MBER precoding aims to minimize BER of the maximum likelihood detection (MLD), on the condition that the transmitter can obtain only imperfect CSI owing to channel estimation and quantization errors of the feedback CSI. The proposed scheme controls its precoding parameters under a transmit power constraint by minimizing an upper bound of BER which is derived from the pairwise error probability and then averaged with respect to the CSI error. Computer simulations demonstrate that the proposed precoding method outperforms a conventional nonrobust MBER precoder and a conventional robust power allocation MBER precoder.
It is known that in cellular systems, the users in cell edge suffer from the interference from interfering cells. In LTE-A, coordinated multi-point (CoMP) processing was proposed to solve the problem. In CoMP, the transmitted/received signals of the users in neighbor cells can be jointly processed such that interference can be either avoided or estimated as desired signals. In the current CoMP operations, precoding is only conducted between individual base-stations and the served user. If we take all the base-stations and the served user into consideration, a network multiple-input-multiple-output (MIMO) system can be constructed. Precoding in such system will have better performance but require a high-dimension codebook which is not supported by current LTE-A systems. In this paper, we first propose a method to solve the problem. The idea is to use the antenna selection technique reducing the number of transmitted antennas such that the existing codebooks can still be used. Existing selection criteria for the maximum likelihood receivers often require sophisticated matrix operations such as QR-decomposition (QRD). Thus, the required computational complexity is high. We then propose some selection criteria without involving matrix operations. Simulations show that while the antenna-selection based precoding method can reduce the feedback overhead and at the same time improve the precoding performance. Also, the performance of the proposed low-complexity criteria is similar to that of the QRD-based criteria.
In this letter, simple power control techniques are proposed to minimize error probability of a two-stream multiple-input multiple-output (MIMO) system with two transmit antennas and a maximum likelihood (ML) receiver, which is known as an optimal receiver but has a high computational complexity problem. The proposed techniques using Euclidean distances of a few error vectors have the advantages of exactly same error performance and very low computational complexity, compared with an optimal power control technique.
In this paper, we propose an adaptive linear precoding technique combined with low complexity iterative detection which can significantly improve the performance of spatial multiplexing multiple input, multiple output (MIMO) systems. By allowing different data stream mappings to the transmit antennas, linear precoding techniques can provide full diversity and increased capacity gain, assuming maximum likelihood (ML) detection is used. There has been previous work on selection criteria to select the appropriate precoding matrix to perform the stream mapping, based on ML or minimum mean square error (MMSE) detection. However these selection criteria were designed under uncoded conditions. In this paper we present a selection criterion based on the Extrinsic information transfer (EXIT) chart specifically designed for a reduced complexity iteratively detected coded system with interference cancellation detection. The results show that the detector maintains full diversity and has performance within 0.4 dB of the ML detector. Moreover precoding increases performance by 1.2 dB compared to the ML detector with fixed stream mapping. In addition it outperforms the SNR criterion from previous work.
In this paper, we propose a novel precoding selection criterion for coded iterative maximum likelihood (ML) detection in spatial multiplexing multiple input, multiple output (MIMO) systems. With the help of this criterion, the adaptive linear precoding technique can significant improve the system performance and provide full diversity by allowing different data stream mappings to the transmit antennas. Previous work had been done on selection criterion to select the appropriate precoding matrix to perform the stream mapping, based on ML or minimum mean square error (MMSE) detection. However these selection criterion were designed under the uncoded conditions. The proposed criterion in this paper can predict the system performance for a particular channel and precoder combination through estimating the mutual information of the convergence point on the Extrinsic information transfer (EXIT) chart, hence can choose the optimum precoder from the codebook to achieve the maximum performance gain. The results show that the system performance is hugely increased by applying the precoding and the particular selection criterion.
This paper proposes a multiple-input multiple-output (MIMO) precoding scheme for the down link of single user (SU) cooperative base station (BS) systems. The proposed precoding scheme mitigates the performance degradation caused by large inter-BS path-loss imbalance and large intra-BS antenna correlation by controlling two parameters. The proposed precoding scheme multiplexes the multiple layers by adjusting the amplitude of each layer, and then decreases the occurrence probability of the small absolute value of the log likelihood ratio (LLR), and so reduces the bit error rate (BER). Link level simulation results show that the proposed precoding scheme decreases the required signal-to-noise ratio (SNR) of BER = 0.001 by 5.5 dB, 2.2 dB, and 0.7 dB in the case of QPSK and coding rate 1/1, 3/4, and 1/2 respectively. The proposed precoding scheme is also evaluated in terms of spectrum efficiency using rank adaptation and adaptive modulation, showing that it improves the spectrum efficiency when the SNR per a receiver antenna is higher than 4 dB.
This paper proposes a MIMO-OFDM precoder that can minimize a BER upper bound of the maximum likelihood detector (MLD) under a non-cooperative downlink multicell co-channel interference (CCI) environment. Since there is no cooperation among base stations (BSs), it is assumed that information on the interference can be estimated at a mobile station (MS) and then fed back to the desired BS for the precoder. The proposed scheme controls its precoding parameters under a transmit power constraint so as to minimize the BER upper bound, which is derived from the pairwise error probability (PEP) averaged with respect to CCI plus noise. Computer simulations demonstrate that the proposed precoder can effectively improve BER performance of cell edge users and is superior in terms of BER to the eigenmode and the minimum mean squared error (MMSE) precoded transmissions which aim to maximize the channel capacity and to minimize MSE, respectively.
